How can I clean up internal geometry?
One way is to select bottom most and top most rim (edge loop) and make them seams. Then switch to face select, select one of external faces on the body and CTRL+L to select linked (it won't work in edge or vertex select modes). This way you will have selected only external geometry. Then you can press CTRL+I to reverse selection and delete faces.
It won't work though if inner geometry is linked somewhere else then on top and bottom with external geometry. If that's the case, the best way would be select face loops one by one with ALT+SHIFT+right click.  After all external faces would be selected, CTRL+I and delete.